Physical shock false inhibitor circuit for simultaneous tone decoder



*ilnited States Patent Oihce 3,473,152 Patented Oct. 14, 1969 3,473,152 PHYSICAL SHOCK FALSE INHIBITOR CIRCUIT FOR SIMULTANEOUS TONE DECODER Richard E. Lunquist and Richard D. Carsello, Chicago, Ill., assignors to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed July 29, 1966, Ser. No. 568,870 Int. Cl. H04q 9/02, 9/10 US. Cl. 340-171 9 Claims This invention relates to a tone responsive circuit and in particular to a tone responsive circuit incorporating a shock inhibitor circuit.

In many electronic devices a series of received tone signals are used to identify and actuate portions of the circuits within the devices. In order to actuate only the desired device and to prevent false actuation, a plurality of tones are usually transmitted at one time. The electronic device may include a plurality of tone responsive circuits which are each responsive only to a single tone frequency. By using a plurality of the tone responsive circuits the device will be actuated only by the plurality of tone signals which identify it.

Many of the tone responsive circuits, and in particular the types employing tuned reeds, are sensitive to mechanical shock which may actuate the tunedreeds producing false tone signals. In the types of devices which employ sequential tone signals the simultaneous development of the false tone signals, due to mechanical shock can be used to prevent false operation of the device. However, in electronic devices in which the plurality of tone signals occur simultaneously the shock inhibitor circuits normally used with the sequential systems cannot be.employed.

It is therefore, an object of this invention to provide a shock inhibitor circuit for tone responsive devices which will distinguish between the smultaneous reception of tone signals and the simultaneous development of tone signals because of mechanical shock. 1

Another object of this invention is to provide a shock inhibitor circuit for a tone responsive device employing simultaneously transmitted tones to prevent false operation when the device is mechanically shocked.

A feature of this invention is the provision of a shock inhibitor circuit for a tone responsive device with means for detecting the envelope of the output of the tone responsive circuits and differentiating the resulting detected signals.

Another feature of this device is the provision of a shock inhibitor circuit for a tone responsive device in which switch means, responsive to the differentiated signal develop a control signal for inhibiting the operaton of the tone responsive device.

The invention is illustrated in the drawings of which:

FIG. 1 is a partial schematic and partial block diagram of a tone responsive device incorporating the mechanical shock inhibitor circuit of this invention;

FIG. 2. shows the output of the resonant reed tone responsive circuit when it is electrically excited;

FIG. 3 shows the output of the resonant reed tone responsive circuit when it is mechanically shocked;

FIG. 4 shows the output of the differentiation circuit. with electrical excitation of the resonant reed circuit; and

FIG. 5 shows the output of the differentiation circuit with the resonant reed circuit mechanically shocked.

In practicing this invention a tone responsive device is provided having tone signal decoder means. The tone signal decoder means acts to receive tone signals and is responsive to a particular tone signal to develop a first output signal. The tone signal decoder means is also re sponsive to mechanical shock to develop a second output signal which is different from the first output signal. The

circuit provides a control signal which is applied to the tone signal decoder to inhibit the same.

Referring to FIG. 1 there is shown a radio paging unit incorporating the circuit of this invention. The radio paging unit is designed to be carried by a person and produces an output singal alerting the wearer only if the received signal contains the proper coding.

Each of the circuits of the unit is powered by voltages designated V V V and V as shown in FIG. 1. In an example of a receiver incorporating the circuit of FIG. 1 the power is supplied by abattery circuit having the following voltages:

Volts v r +2.6 +2.5 V5 +0.8 V; +0.2

The receiver is a single conversion superheterodyne receive Signalsreceived on antenna 10 are amplified in RF amplifier 12 and are coupled to mixer 18 where they are mixed with local oscillator signals generated in oscillator 14 and tripled in frequency in tripler 16. The mixer output is coupled to a series of IF filters and amplifiers 20, 22, 24, 26 and 28. The amplifier IF signal is detected in detector 30 and again amplified in reed driver 32.

The output of reed driver 32 is applied simultaneously to the tone responsive circuits 35, 41 and 42. Ifthe three tones are the proper tones for the particular pager, an output is developed from each of the tone responsive circuits 35, 41 and .42. These outputs are amplified in tone amplifier circuits 45, 40 and 50 respectively and ap plied to tone triggers 56, 70 and 52 respectively. Tone trigger 56 responds to the output of the tone A tone responsive circuit. The output of the tone trigger 56 enables tone trigger 70 which responds to the output of the tone B responsive circuit. Tone trigger 52 is enabled by an output potential from the tone trigger 70 circuit and responds to the signal from tone amplifier 50 to actuate tone oscillator 54. If one or more of the three tones received is not correct, tone scillator 54 is not actuated and the pager does not alert the wearer.

Tone responsi e circuit 35 consists of a resonant reed of the dual coil, single tine type. If a tone signal having a frequency equal-to the frequency of the mechanical resonance of the reed 39 is applied to primary winding 36 reed 39 vibrates strongly, acting as an electromechanical coupling device between primary winding 36 and secondary winding 37. Each reed can be considered to be a very narrow bandpass filter which passes only the desired tone signal. The output of tone responsive circuit 35 is coupled to base 47 of transistor 46 by coil 44. Transistor 46 amplifies the signal and applies the output to tone trigger 56.

Tone trigger 56 consists of transistors 58 and 63 which are both normally cut off when the circuit is in the quiescent condition. When a tone is detected by tone responsive circuit 35 and amplified by transistor 46 the positive swing of the tone signal forward biases transi'stor 58 into conduction. The resultant drop in the voltage at collector 60 of transistor 58 applies a forward bias to base 64 of transistor 63. Transistor 63 conducts and the voltage at collector 65 goes positive. This positive transition is coupled back to base 59 of. transistor 51 through resistor 67 and assures the conduction of tran sistor 58, which in turn causes transistor 63 to be driven into saturation. With transistor 63 in saturation collector 65 approaches the positive potential V, applied to terminal 68. Thus with trigger circuit 56 actuated, a potential is developed which is applied to tone B trigger circuit 70 and to inhibitor circuit 80, via line 78.

Tone B trigger circuit 70 consists of transistors -71 and 72. The potential for operating tone trigger 70 is applied over line 78, to emitter 74 and to base 73 through resistor 77. This potential is derived from tone trigger 56 with transistor 63 saturated. Thus tone trigger 70 cannot operate unless the correct A tone has been received actuating tone trigger 56.

Tone responsive circuit 42, tone amplifier 50 and tone trigger 52 operate in the same manner as the tone A and B circuits. Upon receipt of a C tone an output signal is coupled from tone responsive circuit 42 to amplifier 50. The signal is amplified in amplifier 50 and the amp'lificd signal is applied to tone trigger 52. Tone trigger oscillator 54 causing tone oscillator 54 to produce anoscillatory signal. The oscillatory signal is applied to a speaker 55 to produce a signal audible to the pager wearer.

The above describes the normal operation of the pager when three simultaneous tone signals of the correct frequencies are received. In each case the simultaneous output of the three tone responsive circuits 35, 41 and 42 cause tone oscillator 54 to be actuated producing an audible signal from speaker 55. However, the pager is normally subject to mechanical shocks and vibration. The resonant reed circuits used in the tone responsive circuits of such a device are susceptable to mechanical shock to produce an output even when no input signal is present. Since all the tone reeds are shocked simultaneously a mechanical shock could cause false operation of tone oscillator 54. To prevent this a shock inhibitor circuit 80 is included in the pager;

Referring to FIG. 2 there is shown the waveform 49 of the output signal of tone responsive circuit 35 when it is electrically excited. In FIG. 3, curve 82 is the waveform of the output of tone responsive circuit 35 when it is mechanically shocked. Use is made of the difference in output waveform envelopes to distinguish between a correct electrical excitation and a false mechanical shock.

The envelope of the output signal from transistor amplifier 46, whether mechanically shocked or electrically excited, is detected 'by an envelope detector consisting of diode 86 resistor 85 and capacitor 87. A differentiation circuit 95 consisting of capacitor 88, resistor 90 and the input resistance of transistor 91 couple this signal to base 92 of transistor 91. In normal operation, with no signal present, transistor 91 is conducting and collector 93 is essentially at ground potential.

Referring again to FIG. 2, waveform 96 is the envelope of the electrically excited tone signal which is applied to the dilferentiation circuit 95. In FIG. 4 waveform 98 shows the ditferentiated waveform of the electrically excited tone signal envelope which is at present on base 92 of transistor 91. This slight change in the signal applied to base 92 does not have sutficient amplitude to change the conduction of transistor 91. Thus shock inhibitor circuit 80 does not operate when receiving normal paging signals.

In FIG. 3 waveform 97 is the envelope of the signal produced by mechanical shock. This signal has a sharp negative spike and when differentiated produces a large pulse shown as waveform 99 of FIG. 5. When the signal shown on waveform 99 is applied to base 92 of transistor 91, the conduction of transistor 91 is sharply reduced anda positive pulse is produced at collector 93. This positive pulse is applied to the shock inhibitor multivibrator consisting of transistors 105 and 109.

In the normal standby condition transistor 105 is cut of! and the voltage at collector 106 approaches V volt- 1 age. The voltage at collector 106 is also applied to diode 114 to bias it non-conductive. Also in the standby con dition transistor 109 would conduct to saturation if a supply voltage was available. However, a supply volt-- age is not available until the tone trigger 56 operates which occurs either when a tone of the correct fre-' quency is received or the circuit is mechanically shocked. This potential is applied to collector 112 of. transistor 109 over line 78.

The positive pulse produced at collector 93 of transistor 91 is coupled to base 107 of transistor 105 turning on transistor 105. With transistor 105 conducting the voltage on collector 106 is reduced to near zero p0- tential. The resulting drop in potential on collector 106 is coupled to base 111 of transistor 109 causing this transistor to be cut off. With transistor 109 cut off the potential on collector 112 of transistor 109 rises and this increase in potential is coupled back to base 107 of transistor 105 through resistor 116. Thus the potential on collector 106 is maintained near zero potential as long as an output potential is supplied from trigger circuit 56. The negative going signal on collector 106 of transistor 105 is coupled through capacitor 118 to base 92 of transistor 91. This feedback acts to vproduce a more positive action in the output circuit and causes the input pulse applied to base 92 of transistor 91. to appear as shown in waveform 119 of FIG. 5.

The zero potential on collector 106, with the inhibitor circuit in operation, is coupled through diode 114 to a base 69 of transistor 71. This acts to clamp base 69 at a potential near zero to bias transistor 71 to nonconduction. This prevents signals from tone responsive circuit 41 and amplifier transistor 43 .from actuating trigger circuit 70. With trigger circuit 70 biased so that it cannot operate no potential is developed to permit tone trigger 52 to actuate tone oscillator 54 and no output tone will be developed.

Thus inhibitor circuit acts to clamp the trigger Cll" cult of the tone B circuit to prevent its operation in the event the pager is mechanically shocked. By distinguishing between the waveforms resulting from electrical excitation and mechanical shock the inhibitor circuit permits operation of pager when the correct electrical tone signals are received. When false tone signals are received.

due to mechanical shock, the inhibitor circuit prevents operation of the pager.

The following component values have been found use ful in a circuit of FIG. 1. However, the component values are not limited to those listed.

1. A shock inhibitor circuit for a tone responsive de= vice having tone signal decoder means adapted to receive at least one tonesignal and being responsive thereto to develop a first output signal, the tone signal decoder means further being responsive to mechanical shock to develop a second output signal different from said first output signal, and first circuit means coupled to the tone decoder means and responsive to the first and second output signals to be actuated thereby, said shock inhibitor circuit.

including in combination, detector means coupled to said tone signal decoder means for receiving the first and sec= 0nd output signals, said detector means being responsive to the second output signal only to develop a control sig nal, second circuit means coupling said detector means to the-tone signal decoder means for applying said conthe tone signal decoder means whereby the first and second output signals are blocked from the first circuit means.

2. The shock inhibitor circuit of claim 1, wherein said detector means includes envelope detector circuit means coupled to said tone signal decoder means, said envelope detector circuit means being responsive to said first and second output signals to produce first and second detected signals respectively, dilferentiation means coupled to said envelope detector circuit means and responsive only to said second detected signal to develop a pulse signal, third circuit means coupled to said dilferentiation means and responsive to said pulse signal to develop said control signal.

3. The shock inhibitor circuit of claim 2, wherein the tone signal decoder means is further responsive to the tone signal and the mechanical shock to develop an output potential, for the duration of said tone and shock signals, said third circuit means includes multivibrator means coupled to the tone signal decoder means and said differentiation means and having first and second states, said multivibrator means normally being in said first state and acting in said second state to develop said control signal, said multivibrator means being responsive to said pulse signal to assume said second state and being responsive to said output potential to be maintained in said second state for the duration of said output potential.

4. A shock inhibitor circuit for a tone responsive device having first tone circuit means adapted to receive a tone signal input comprising a plurality of simultaneously transmitted tones and including resonant reed tone filter means and trigger circuit means, the resonant reed tone filter means being responsive to one of the transmitted tones to develop a first output signal and further being responsive to mechanical shock to develop a second output signal different from the first output signal, the trigger circuit means being coupled to the resonant reed tone filter means and responsive to the first and second output signals to develop an output potential, second tone circuit means coupled to the trigger circuit means and being adapted to receive the tone signal input, the second tone circuit means being responsive to the output potential and a different one of the plurality of simultaneously transmitted tones to develop an actuating signal and furtherv being adapted to be rendered inoperative in response to a control signal applied thereto, said shock inhibitor circuit including in combination, detector means coupled to said resonant reed tone filter means and responsive to said second output signal only to develop a pulse signal, switch means coupled to said detector means and being responsive to said pulse signal to generate the control signal, and circuit means coupling said switch means to the second tone circuit means for applying the control signal thereto whereby said second tone circuit means is rendered operative.

5. The shock inhibitor circuit of claim 4, wherein said detector means includes, envelope detector means for developing detected signals representative of the envelopes of the first and second output signals and differentiation means coupling said envelope detector means to said switch means and responsive to said second outpuhsignal only to develop said pulse signal.

6. The shock inhibitor circuit of claim 5 wherein said switch means includes, multivibrator means having first and second operating states and being coupled to said differentiation means and the resonant reed tone filter means, said multivibrator means normally being in said first operating state and acting in said second operating state to develop said control signal, said multivibrator means being responsive to said pulse signal to assume said second operating state and further being responsive to the output potential to remain in said second state for the duration of the output potential, said circuit means coupling said multivibrator to the second tone circuit means for applying the control signal thereto whereby the second tone circuit means is rendered inoperative.

7. The shock inhibitor circuit of claim 5 wherein said envelope detector means includes diode means coupled to said resonant reed tone filter means, first capacitance means coupled between said diode means and a first reference potential and first resistance means coupled between the junction of said diode means and said first capacitance means and a second reference potential, said differentiation means includes second capacitor means coupled to said first resistance means and the junction of said diode means and said first capacitance means, second resistance means coupled to said second capacitance means, and a first transistor coupling said second resistance means to said switch means.

8. The shock inhibitor circuit of claim 7 wherein, said first transistor includes an emitter electrode connected to said first reference potential, a collector electrode coupled to said switch means and a base electrode, coupled to said second resistance means, third resistance means coupled between the junction of said second capacitance means and said second resistance means and said second reference potential, and third capacitance means coupled between said switch means and said base electrode, said third capacitance means being responsive to the generation of said control signal to couple a feedback signal to said base electrode.

9. The shock inhibitor circuit of claim 7 wherein, the second tone circuit means includes a second transistor having an emitter electrode coupled to said first reference potential and a base electrode, second diode means coupling said switch means to said base electrode of said second transistor for applying said control signal thereto, said second transistor being responsive to said control signal to be biased to nonconduction whereby the second 1 tone circuit means is rendered inoperative.

References Cited UNITED STATES PATENTS US. Cl. X.R. 

4. A SHOCK INHIBITOR CIRCUIT FOR A TONE RESPONSIVE DEVICE HAVING FIRST TONE CIRCUIT MEANS ADAPTED TO RECEIVE A TONE SIGNAL INPUT COMPRISING A PLURALITY OF SIMULTANEOUSLY TRANSMITTED TONES AND INCLUDING RESONANT REED TONE FILTER MEANS AND TRIGGER CIRCUIT MEANS, TO RESONANT REED TONE FILTER MEANS BEING RESPONSIVE TO ONE OF THE TRANSMITTED TONES TO DEVELOP A FIRST OUTPUT SIGNAL AND FURTHER BEING RESPONSIVE TO MECHANICAL SHOCK TO DEVELOP A SECOND OUTPUT SIGNAL DIFFERENT FROM THE FIRST OUTPUT SIGNAL, THE TRIGGER CIRCUIT MEANS BEING COUPLED TO THE RESONANT REED TONE FILTER MEANS AND RESPONSIVE TO THE FIRST AND SECOND OUTPUT SIGNALS TO DEVELOP AN OUTPUT POTENTIAL, SECOND TONE CIRCUIT MEANS COUPLED TO THE TRIGGER CIRCUIT MEANS AND BEING ADAPTED TO RECEIVE THE TONE SIGNAL INPUT, THE SECOND TONE CIRCUIT MEANS BEING RESPONSIVE TO THE OUTPUT POTENTIAL AND A DIFFERENT ONE OF THE PLURALITY OF SIMULTANEOUSLY TRANSMITTED TONE TO DEVELOP AN ACTUATING SIGNAL AND FURTHER BEING ADAPTED TO BE RENDERED INOPERATIVE IN RESPONSE TO A 